The invention relates to a circuit assembly for producing a one-way connection between a first transmitter or receiver operating on a first frequency and an antenna, on the one hand, as well as between a second transmitter or receiver operating on a second frequency and the antenna, on the other, each transmitter or receiver having a port for producing a connection to the antenna.
When several transmitters and/or receivers are connected to an antenna for radiating transmission signals via the antenna or receiving reception signals via the antenna, a connection needs to be made only between the transmitter and/or receiver in operation at the time and the antenna whilst the other units are disconnected from the antenna and remaining units. The classic case in such an arrangement is the connection of an antenna to a transmitter and to a receiver, this connection being made via an antenna diplexer which in the transmission mode ensures a connection exists only between the transmitter and the antenna, whilst in the receiving mode it connects only the receiver to the antenna. This selection or disconnection function is conventionally done with the aid of diode switches signalled ON/OFF by separate control signals. These diode switches complicate the circuitry required for the control.
One aspect of the invention is based on the object of configuring a circuit assembly of the aforementioned kind which achieves the desired selection or disconnection effect between the units to be connected to/disconnected from the antenna in each case exclusively by passive means.
In accordance with this aspect of the invention this object is achieved by a filter having at least one symmetrical port, the passband of which covers the first and the second frequency, whereby the antenna is connected to one of the ports of the filter, a first passive network between one lead of the at least one symmetrical port of the filter and the port of the first transmitter or receiver which short-circuits at the second frequency the input of the first transmitter or receiver, and a second passive network between the other lead of the at least one symmetrical port of the filter and the port of the second transmitter or receiver which short-circuits the input of the second transmitter or receiver at the first frequency.
In the circuit assembly in accordance with an aspect of the invention a filter comprising at least one symmetrical port is inserted between the antenna and the transmitters and/or receivers. This configuration of the filter permits connecting one unit to the one lead of the symmetrical port and the other unit to the other lead of the symmetrical port. The passive networks connected by the leads of the symmetrical ports of the filter ensure that, depending on the frequency existing at the time, the one or the other unit is connected to the antenna, whereby the connection of the other unit in each case is short-circuited so that it is disconnected. By using passive networks no separate circuiting means are needed in addition to make the desired connection of the unit in operation at the time to the antenna whilst simultaneously disconnecting the other unit from the antenna.
Advantageous further embodiments of the invention are characterized in the sub-claims.
A preferred aspect is a transmitter and the other unit is a receiver, the combination of the filter with the symmetrical port and the passive networks handles the classic task of an antenna diplexer which ensures that only the unit in operation at the time is connected to the antenna whilst the other unit is disconnected. In another preferred aspect the passive networks are simple series resonance circuits which are simple to realize and which require no extra circuitry for their control.